The correct answer is option 4, Chanhudaro. Chanhudaro was the only Indus city that did not have a citadel. A citadel was a fortified area within the city that served as a defensive structure. It was typically located on a raised platform and was used for protection against potential attacks.

Kalibangan (option 1), Harappa (option 2), and Mohenjodaro (option 3) were all Indus cities that had citadels. These citadels were important features of the urban planning and architecture of the Indus Valley Civilization. However, Chanhudaro did not have a citadel, which sets it apart from the other cities. The absence of a citadel in Chanhudaro suggests that it may have had a different kind of urban layout or defensive strategy compared to the other Indus cities.